Editor's note: This is the third in a series of regional looks at the most competitive House and Senate races to watch in 2016. The Mid-Atlantic region includes Delaware, Maryland, New Jersey, New York, Pennsylvania and West Virginia.Pennsylvania Senate: Democrats are on a quest to gain five seats and the Senate majority, and the Keystone State looks like one of the key contests. Republican Patrick J. Toomey defeated Democrat Joe Sestak in 2010, 51 percent to 49 percent. Even though some Democrats are unconvinced Sestak is the best candidate for 2016, no credible alternative has emerged, and the former congressman looks likely to be the nominee once again. Skepticism about Sestak doesn’t mean he can’t win. The Democrat will be a credible nominee and gets the chance to run in a presidential year this time, when Democratic turnout should be better. The Rothenberg & Gonzales Political Report /Roll Call rates the race as a Tossup/Tilts Republican .

New York’s 24th District: Republican John Katko defeated Democratic Rep. Dan Maffei, 58 percent to 40 percent, in one of the late-breaking races of 2014 and with one of the most stunning margins of victory. Katko now represents a district which President Barack Obama won with 56 percent in 2008 and 57 percent in 2012. Democrats are still searching for a challenger after Syracuse Mayor Stephanie Miner declined to run. But this is a top-tier takeover target and a must win for House Democrats. The Rothenberg & Gonzales Political Report /Roll Call rates the race as a Pure Tossup .

Pennsylvania’s 8th District: Democrats targeted GOP Rep. Michael G. Fitzpatrick early last cycle and their nominee fell short, 62 percent to 38 percent. But Fitzpatrick is honoring his self-imposed term-limit pledge and is not running for re-election, leaving Democrats with a good takeover opportunity. Mitt Romney won the district by less than 1 percent in 2012, but Obama won it by 7 points in 2008. Democrats will have a competitive primary between state Rep. Steve Santarsiero and small-business owner Shaughnessy Naughton (who ran a competitive race in last year’s primary). Republicans are likely to sort out their field behind closed doors. But the general election is expected to be competitive and another must-win for Democrats. The Rothenberg & Gonzales Political Report /Roll Call rates the race as a Tossup/Tilts Republican .

New York’s 19th District: GOP Rep. Chris Gibson demolished self-funding Democrat Sean Eldridge, 63 percent to 35 percent, last year in this competitive district. But Gibson is not seeking re-election. Because his decision was a surprise to virtually everyone, the candidate fields have been slow to develop. Republicans may face a divisive primary while Democrats are searching for a quality contender. Obama won the district by at least a handful of points so the 19th District should be close to the top of Democratic takeover lists. The Rothenberg & Gonzales Political Report /Roll Call rates the race as a Pure Tossup .

Maryland Senate: Long-time Democratic Sen. Barbara A. Mikulski is retiring, but the race to watch to replace her is the Democratic primary. Rep. Chris Van Hollen, whom many regarded as a future speaker of the House, is running, along with Rep. Donna Edwards. The field is still void of a Baltimore candidate, and it’s unclear if Rep. Elijah E. Cummings or someone else will take the plunge. Rep. John Delaney, who like Van Hollen represents part of Montgomery County, hasn’t announced his plans, but he has the luxury of time because of his personal wealth. Republicans aren’t likely to seriously contest the general election unless chaos breaks out on the Democratic side. The Rothenberg & Gonzales Political Report /Roll Call rates the race as Safe Democrat .